Finned heat exchanger



Dec. 21, 1965 F. w. STAUB ETAL 3,224,504

FINNED HEAT EXGHANGER Filed Dec. 25, 1963 I HOT GAS lN 23 l 24 A l lGl l j; 2o l EXHAUST FIG. 2

FIG?) 33 HOT GAS IN INVENTORS FRED W STAUB BY LEE H. TOMLINSON ATTORN EY United States Patent Ofiice 3,224,504 Patented Dec. 21, 1965 3,224,504 FINNED HEAT EXCI-IANGER Fred W. Stauh and Lee H. Tonilinson, Schenectady, N.Y., assignors to General Electric Company, a corporation of N ew York Filed Dec. 23, 1963, Ser. No. 332,489 3 Claims. (Cl. 165-485) This invention relates to a heat exchanger and, more particularly, to a heat exchanger of the type employing fins.

In many applications it is imperative that heat, transferred by means of a gaseous medium, be distributed uniformly over the surface to be heated. This is to be accomplished without the sacrifice of eificiency of heat transfer and in such a manner as to maintain the pressure drop, weight and expense as low as possible. Prior art heat exchangers have failed to achieve these desirable characteristics to a fully satisfactory degree.

Accordingly, it is one object of the present invention to provide a lightweight, finned heat exchanger which eificiently and uniformly transfers heat from a high temperature source to a low temperature base member.

It is a further object of the present invention to provide a finned heat exchanger including improved means for controlling the flow of hot gases in heat exchange relationship therewith with a minimal pressure drop.

Further objects and attendant advantages of the present invention will become better understood from the following description.

Briefly stated, this invention in one form provides a finned heat exchanger designed for efiicient and uniform heat transfer over the entire area of the heat exchanger base plate to which the heat is to be transferred. A plurality of passage-forming fins are attached thereto for conducting heat from a source to the base plate. The fins comprise a plurality of parallel heat transfer elements, each element including two concentric rows of longitudinally spaced tubular heat exchange members. The discontinuity of each row caused by the longitudinal spacing of the tubular members provides a conduit having a plurality of axially spaced interstices. The interstices of the outer row are longitudinally displaced relative to the interstices of the inner row thus forming a plurality of small, separate gas flow passages between the two rows, the passages being parallel to the base plate. Heat from the hot gas is transferred to both rows of tubular members and, in turn, is uniformly transferred to the base plate.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention will become better understood from the following description taken in combination with the accompanying drawing in which:

FIGURE 1 is an end of a heat exchanger formed in accordance with a first embodiment of this invention.

FIGURE 2 is a cross-sectional view taken along line 2-2 of FIGURE 1.

FIGURE 3 is an end view of a heat exchanger formed in accordance with a second embodiment of this invention.

FIGURE 4 is a cross-sectional view taken along line 4-4 of FIGURE 3.

With reference to the drawing and, more particularly, FIGURES l and 2, a heat exchanger 10, formed in accordance with the first embodiment of the present invention, includes a base member or plate 12 having a plurality of fins in the form of parallel heat transfer elements 14 mounted on one surface thereof. For purposes of discussion, it is assumed that heat is to be transferred from a heat source (not shown) to the base plate 12 by means of a gaseous heat transfer medium.

In order to provide efficient and uniform distribution of heat over the base plate 12, the heat transfer elements 14 are formed and placed so as to provide a plurality of small, separate gas flow passages 16 directing the gas from the heat source to an exhaust system (not shown). One method for providing the gas flow passages is to form each element 14 from two concentric and radially spaced rows 18, 21 of longitudinally aligned tubular heat exchange members, the tubular members of the radially outer row being designated as 21 and the tubular members of the radially inner row being designated as 22. In order to have the outer row and inner row tubular members 21, 22 respectively in direct contact with the base plate 12 for heat exchange purposes, the outer row tubular members 18 are made partially circular in cross section, i.e. they form a major arcuate portion of a circle as may be seen in FIGURE 1. The inner tubular members 20 have a completely circular cross section.

The tubular heat exchange members of each row are aligned and axially spaced from one another to form a plurality of axially spaced interstices, the interstices of the outer row 18 being designated as 23 and the interstices of the inner row 20 being designated as 24. The interstices provide inlets between adjacent tubular members to permit gas flow into and axially though the tubular members. As may be seen in FIGURE 2, the interstices 23 of the outer row 18 are axially displaced relative to the interstices 24 of the inner row 20. By offsetting the interstices of the two rows 18, 20 there is formed a plurality of the aforementioned annular gas flow passages 16 between the two rows. A portion of the incoming hot gas flows from each interstice 23 of the outer row 18 axially along the entire length of the heat transfer element 14 through the annular passages 16 between the outer row 18 and the inner row 20. Additionally, a large portion of the incoming hot gas flows through the annular passages 16 and then inwardly through the inner row interstices 24 and axially through the inner row 24 to the exhaust system located at one end thereof. It can be seen that by this arrangement the incoming gas flow is divided up into many small, separate flow streams distributed uniformly over the base plate 12.

The particular dimensions of fin length and diameter and passage cross-sectional area determine the pressure drop along the flow path and these dimensions, along with the thickness of the tubular members and the particular material employed for fabricating the tubular members and base plate, determine the heat transfer efiiciency. To maximize the heat transfer efficiency and uniformity, the particular dimensions are chosen in order for a major percentage of the pressure drop to be taken through the plurality of individual flow passages 16 with the length of each passage being designed to comprise only a small percentage of the total base plate length. It has been found that a heat exchanger, formed in accordance With the dimensions listed below, has an efficiency of -95 percent, and requires a pressure drop less than 0.01 of an inch of water. Preferably percent, or in any event at least 70 percent, of the total pressure drop is taken through the individual flow passages 16. Furthermore, each passage length is designed to be preferably less than 10 percent, or at most 30 percent, of the total base length. The flow passage and interstice dimensions are maintained equal throughout the length of the base plate 12 to pro vide equal inlet and exit hot gas temperatures and flow rates which results in uniform heat transfer to the base plate. A heat exchanger producing these results was produced having the following characteristics: Total length of each heat exchange element 4.0". Tubular member wall thickness 0.020". Inside diameter of outer tubular member 0.765. Inside diameter of inner tubular member 0.625". Total base length 4.0". Number of tubular members per row 8. Number of parallel heat exchange elements 8. Distance between parallel heat exchange elements 0.25. Tubular member and base material Copper.

A heat exchanger 28 formed in accordance with a second embodiment of this invention is illustrated in FIG- URES 3 and 4. The heat exchanger 28 comprises a plurality of parallel heat transfer elements 30 mounted on one side of and in heat exchange relationship with a base plate 32. Each element 30 includes a series of axially spaced tubular cylinders 33. Projecting outwardly from the outer surface of and at both ends of each cylinder 33 is an annular fin 34. This arrangement provides a plurality of gas flow passages 36 between each pair of adjacent fins 34, the passages 36 being aligned with and communicating with interstices 38 formed by the axial spacing of adjacent tubular cylinders 33. Hot gas, admitted into each of the passages 36 in a direction toward the base plate 32, flows through each passage 36 and into and axially through the cylinders 33 toward one end thereof. As with the first embodiment of FIGURES 1 and 2, preferably 90 percent, or in any event at least 70 percent, of the pressure drop is consumed through each passage 36 formed by the annular fins 34. Also, the length of each passage is maintained preferably less than percent, or at most 30 percent, of the total base length. Additionally, the passages all have the same dimensions so that the inlet and exit temperatures of the hot gas and the flow rate for each passage 36 are equal in order to provide uniform heat distribution over the base plate 32.

Heat exchangers formed in accordance with the abovedisclosed embodiments distribute heat across a base plate with high heat transfer efliciency and uniformity accompanied by a low total pressure drop. These heat exchangers are easy and relatively inexpensive to fabricate. Because of the spaced relationship between adjacent tubular members, relatively stress-free heat-conducting fins and gas flow conduits are provided. The particular characteristics with regard to pressure drop and total heat transfer capabilities may be varied by varying the dimensions of the particular elements of the heat exchanger, that is, by controlling the dimensions of the gas flow passages.

While two specific embodiments have been shown and described above, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects. Therefore, it is intended in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A heat exchanger comprising:

(a) a base member,

(b) a plurality of generally tubular members mounted in axial alignment on a surface of said base member in heat exchange relationship therewith, said tubular members being closely spaced to form interstices therebetween, and

(c) means including a plurality of spaced conductive annular disks, one of said disks being mounted on and extending outwardly from each end of said tubular members to form a plurality of fluid flow passages communicating with said interstices, the length of each of said passages being no more than 30 percent of the total length of the base member, the fluid flowing through said passages, said interstices and said tubular members to form heat exchange flow paths, the temperatures of the fluid entering each of said passages being equal respectively and the pressure drop along the length of each of said passages being at least 70 percent of the total pressure drop along the entire flow path.

2. A heat exchanger comprising:

(a) a base member,

(b) a plurality of first generally tubular members mounted in axial alignment on a surface of said base member in heat exchange relationship therewith, said first tubular members being closely spaced to form interstices therebetween, and

(c) a plurality of second generally partially tubular members radially spaced from and concentric with said first tubular members and mounted on said surface of said base member in heat exchange relationship therewith, said second tubular members being axially closely spaced at intervals offset relative to the spacing of said first tubular members to form a plurality of annular fluid flow passages between said first and second tubular members communicating with said interstices, the length of each of said passages being no more than 30 percent of the length of the base member, the fluid flowing through said passages, said interstices and said first and second tubular members to form a heat exchange flow path, the temperatures of the fluid entering each of said passages and leaving each of said passages and the flow rate through each of said passages being equal respectiveiy and the pressure drop across each of said passages being at least 70 percent of the total pressure drop along the entire flow path.

3. A heat exchanger comprising:

(a) a base member,

(b) a plurality of first generally tubular members mounted in axial alignment on a surface of said base member in heat exchange relationship therewith, said first tubular members being closely spaced to form interstices therebetween, and

(c) a plurality of second generally partially tubular members radially spaced from and concentric with said first tubular members and mounted on said surface of said base member in heat exchange relationship therewith, said second tubular members being axially closely spaced at intervals offset relative .to the spacing of said first tubular members to form a plurality of annular fluid flow passages between said first and second tubular members communicating with said interstices, the length of each of said passages being no more than 10 percent of the length of the base member, the fluid flowing through said passages, said interstices and said first and second tubular members to form a heat exchange flow path, the temperatures of the fluid entering each of said passages and leaving each of said passages and the flow rate through each of said passages being equal respectively and the pressure drop across each of said passages being at least percent of the total pressure drop along the entire flow path.

References Cited by the Examiner FOREIGN PATENTS 7/1954 Canada. 5/ 1908 Switzerland. 

1. A HEAT EXCHANGER COMPRISING: (A) A BASE MEMBER, (B) A PLURALITY OF GENERALLY TUBULAR MEMBERS MOUNTED IN AXIAL ALIGNMENT ON A SURFACE OF SAID BASE MEMBER IN HEAT EXCHANGE RELATIONSHIP THEREWITH, SAID TUBULAR MEMBERS BEING CLOSELY SPACED TO FORM INTERSTICES THEREBETWEEN, AND (C) MEANS INCLUDING A PLURALITY OF SPACED CONDUCTIVE ANNULAR DISKS, ONE OF SAID DISKS BEING MOUNTED ON AND EXTENDING OUTWARDLY FROM EACH END OF SAID TUBULAR MEMBERS TO FORM A PLURALITY OF FLUID FLOW PASSAGES COMMUNICATING WITH SAID INTERSTICES, THE LENGTH OF EACH OF SAID PASSAGES BEING NO MORE THAN 